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Keeping clean water on tap

After water has been treated at the purification plants, it comes out so pure that it can leach minerals from the metal pipes in the distribution network. Researchers are testing various concentrations of minerals to add to the super-pure water so it will neither corrode the pipes nor form mineral deposits on them.

Nanoparticles - tiny particles of materials like silver and gold, a fraction of the size of a virus - have special properties. They can be used in antibacterial coatings, to kill tumours, or to deliver drugs.

But they can be a double-edged sword.

The same properties that enable them to enter and kill cancer cells or bacteria also mean they can be toxic to healthy cells in the wrong context.

The use of nanoparticles has become more widespread in recent years, and they can be found in thousands of consumer products ranging from sunscreen to food packaging.

Scientists have yet to fully understand where these particles end up, and their effect on human and environmental health.

That's why researchers at the National University of Singapore (NUS) and Hebrew University of Jerusalem are working together on how best to detect and remove such nanoparticles from water, especially using low-cost, readily available materials.

Professor Suresh Valiyaveettil of the NUS chemistry department said silver nanoparticles have been shown to kill cells and cause abnormalities in zebrafish, the guppy- size fish popular in toxicity testing because their reactions are similar to humans'.

Increased use of nanoparticle products will increase the concentration of nanomaterials in the environment, particularly water, if their manufacturers do not deal properly with waste, he added.

Prof Suresh said: "The next question that came up in our mind was, 'How do we remove such contaminants from the water supply?' How do we detect these tiny particles in contaminated water? Do the existing methodologies of water purification remove these emerging contaminants?"

So he and his colleagues worked with a water treatment expert, Professor Avner Adin, of the Hebrew University of Jerusalem.

Earlier this year, they found that apple and tomato peel and other food wastes like sugar cane residue and soybean hulls could be used to remove nanoparticles and other contaminants from water.

They also found that nanoparticles clung to the surface of metal oxides like zinc oxide (the white powder commonly used in zinc sunscreens), and suggested that the nanoparticles could be clinging to charged areas on the surface of the oxide particle.

"All materials used in our lab are relatively easy to get in large amounts and can be modified to fit the need of certain communities," he said.

Now the researchers are looking for collaborators for field trials of these materials, Prof Suresh said.